HELP, oil temp/pressure gauge problems.

In my 81' Vette, lights off all gauges work fine except oil temp automatically buries. Lights on, oil pressure automatically buries, but if I turn the dimmer down they return to reading correctly. Weird huh? Hate to just start replacing sensors if it's a ground issue. And where do the gauges ground ? Thanks in advance...

Sounds more like you have a short between the lite and oil guage.